How do resistors react in an LED-Array? Answered

Hey guys. I've been reading myself through a lot of articles on websites about how resistors and LED's work, but what I still don't understand is why, when calculating the required resistors for an LED-Array, this website ( ) takes maximum 4 LED's for each resistor at 9V and a diode forward voltage of 2.0 - is it to prevent it become unstable or something like that? And frankly, I think that I miss understand resistors, although I've read a lot of articles about it. So, what I think resistors do is this: Since resistors are used in a simple 1-LED-circuits that has more voltage than the diode forward voltage, it simply lowers the voltage to  the desired forward voltage ( 2.0 for a Red-LED as far as I remember ) - so my point is, when it always is lowered, why would you need more resistors when the voltage is lowered from the first LED on? Perhaps I am very bad at explaining my logical problem here, but I hope that someone actually understands something out of this mess. xS

Asked by Zrodo 6 years ago


Which things I need to know to study relativity theory? And any good book to study it?

Asked by Ahtasham Ahmad Mohtashim 4 years ago

"Growing Earth" theory ...

Hi.I was wasting some time on Google Video, and I found this one.This man believe Earth (and others planets) are expanding ...According to Wikipedia, this theory is not new, and is serious. After all, if the Sun (and stars) grows, why not the "core" of planets too ?

Posted by chooseausername 10 years ago

Another theory...

I was wondering if this is doable, or even practical for that matter. So I read up on lasers and from what I can tell it is a form of light in which the wave frequencies are perfectly aligned. So I was wondering if you aligned UV light wave frequencies, would you get a laser that would burn stuff, and not to sound morbid, but in high quantaties, kill people. (Only for the sheer exitement of figuring something out am I posting this. I do not in any way want to kill someone.)

Posted by vroom...vroom... 6 years ago

Unified field theory?

I was windering if someone could tell me how to add gravity to the Unified field theory? thanks

Asked by RelyNupon 9 years ago

Music Theory 101

Hello, i got an idea of making a series of detailed, yet easy to understand instructables on music theory. i mean music theory, and i mean things you would learn in college level class. i preety much dedicated most of my life to music theory, piano, cello, and listening, as well as analyzing written music. i have also had great teachers that thought me a lot of things about music and life, and i would only feel like the greatest asshole alive if i didnt share them. one thing that is special to music theory, and only to music theory, is that it is a field of study that originated from art, not vice versa. those instructibles would cover preety much everything involved with music, including the mathematics and physics that go with it! history will be included too! the reason why i'm posting it here, is to see how many people are interested, who would want to help out, and to look for reccomendations and requests. my resume: 5 years piano 4 years cello 9 years music theory perfect pitch played in 4 different orchestras considering starting doing a chamber music program, orchestras are getting boring now :D im part of the Tri-M music honor society and i volunteer sometimes. PLEASE REPLY WITH WHAT YOU THINK ABOUT THIS PROJECT :D music theory

Posted by macplo 9 years ago

How does radio really work?

             I'm studying to take the exam for a technician class ham radio license, and have been reading up for it.  However, the book just gives practice, not theory.  For example, it says that radio energy is carried down a coaxial, window, etc. cable between the two conductors, but it doesn't say how this actually happens or works.  I know what radio does, but I'm a little lost when it comes to theory regarding its transmission, being carried in cables, filtering, SWR, etc.  Answers are appreciated.  Thanks!

Asked by mad magoo 8 years ago

Earth Ground?

           Well, it seems about time to add to my list of electrical theory questions with answers far too broad for one question, so:                          I understand that the Earth can act as a giant capacitor, conductor, etc.  What I don't understand is why.  For instance, why would ac power from the hot wire dissipate into the ground?  (and, for that matter, will power from the neutral wire not do so?  If so, why?)   

Asked by mad magoo 8 years ago

My theory...

So here is my theory. If you did all the math, (which I did),  and made a syrup of the exact viscosity. Would that syrup flow like water underwater just like water flows in air. Here is a diagram with all the math there for you.   I created a simple ratio... the number at the bottom right is my perfect syrup viscosity.

Posted by vroom...vroom... 6 years ago

Is it possible to draw energy from an ion chamber?

On a purely theoretical basis, would it be possible to harness a small sample of radioactive material and an ion chamber to produce a small trickle of electricity? I'm not sure what the practical use of a device would be, and I'm well aware of the risks and dangers involved; I'm asking to satisfy my own curiosity.

Asked by jlensher 6 years ago

would this work for a homemade generator?... like getting a dc motor and turning it in reverse ?

Instead of spinning the moro by connecting it to a battery spin it on the spindle that turns? would it work

Asked by sharlston 8 years ago

theory of water rocket?

Asked by ainmiey 6 years ago

How do I determine the size of the image needed to reflect onto a cylinder (see Q for better description)? Answered

I plan to take a large disc shaped screen and then reflect that image onto a cylinder to create a holographic effect. Right now this is just a concept but I am wondering if this is plausible and what size the disk would need to be to create an image to cover the cylinder. If a formula could be provided that would be best or just a general explanation of how to find a formula.

Asked by TheTechGuy99 7 years ago

Theory, execution and actual construction of a 'Bullet-Shot Location' like system Answered

 How could it be done? I have revised a version using only two microphones that once one of the microphones 'hear'  the sound, a timer will start and will stop once the next microphone 'hears' it.  This would essentially enable you to draw a line straight down the middle of the gun. It would also allow for tracking the location in real-time. How could you physically build it for a cheap set-up. I'll upload a couple of diagrams some time.

Asked by Lance Mt. 8 years ago

Why can a function satisfying same boundary conditions as functions Un(x) of a complete set be expanded as ΣCnUn(x)?

This is a question I encountered while reading Introduction to Quantum Theory by Hendrik F. Hameka (Please don't worry, I'm not trying to cheat on my homework, I am just asking out of curiosity). The book states the following:      "It can be shown that a function f(x) that satisfies the same boundary conditions as the functions Un(x) of a complete set can be expanded as f(x) = Σ CnUn(x) ... If we multiply by U*m(x) and integrate, we obtain Um | f > = Cm " This second part is fairly straightforward because ∫ U*m f(x) dx = ∫ U*m Σ CnUn(x) dx and it follows that Um | f > = Cn Σ Um | Un > = Cn Σ δn,m = Cn However, the first part confuses me because I can only justify it when Un(x) = (2π)^(-1/2) e^(inx) (The example of a complete set given in the book, actually) In that case, it can easily be seen that the expression Σ Un | f > Un(x) is just the Fourier Series expansion of f(x) and thus the result is valid for the particular complete set. However this does not explain why this is valid for all complete sets: "how can you prove that this conclusion is valid not only for this particular complete set, but for all complete sets?" is my question. Thank you in advance for answering! Please feel free to post any questions of your own if you need clarification. Also, please be advised that you should not post responses on the order of "you didn't specify an interval of integration, so your question is impossible!" - if you know enough to answer the question, then you will understand why said interval is not specified, etc. Once again, thanks!

Asked by Xellers 8 years ago

How to measure open loop H(s)? Answered

When designing constant current linear dummy loads, and when I was (attempting) to design a really nice linear power supply with op amps and pass transistors, I consistently run into the devil of the circuits that incorporate feedback. INSTABILITY! Especially if I use fast op amps, or MOSFETs, etc. My understanding as to why this happens is because I still have some positive gain at the point at the frequencies where signal the total loop has that dreaded -180 degree phase (gain margin) and then where the gain is unity and phase is at -180, again allowing that frequency component to be successively amplified (or never attenuated) as that wave whirls around the loop. However, with op amp circuits, how am I supposed to get an accurate open loop measurement, when the DC gain is so stupidly high the input to an op amp is essentially a comparator? This article suggests whacking in a 20 ohm resistor and injecting a signal into it, and measuring the voltage on either side of it (?) How is this supposed to work? Is there a better method in something like LTspice?

Asked by -max- 8 months ago

Big Bang "theory" Dbunked!


Posted by slasinski 11 years ago

Old Phone That Can Play Games? Ideas...

Hi guys, so I was recently talking with my friend Omar about random stuff, and (like always) our conversation somehow got really off track and we ventured into the history of old phones (Nokia 3310...breaking everything we touch since 2000). We somehow got to thinking about how old bar style phones could be useful for the making community. My thought (which I incidentally shouted out as loud as a human can go) was this: what if we could put a really basic game onto the phone? Would it be possible with the current hardware? Maybe...and the controls are there, most phones have a D-pad with 12 keys (which could be special function keys in the game). I was thinking of games along the line of Doom, or any old FPS game...but in retrospect, that would be ambitious, and to be practical, a stick man game would probably be the minimum.  So my questions are: a) would it be possible for the hardware on the phone to be wiped of all software and would it be good enough to support the code. b) is it even possible to reprogram the phone, or even get some sort of bootloader onto the device? Probably not. And if not, is there any other way to put a game or any file onto the phone's hardware... I guess that's it. In general, would it be possible, and if yes, could anybody give me a few starters so I could try to do it? Thanks, Ivan

Posted by IvanT3 3 years ago

String Theory,..this is not detailed, but what do you think?

Here is a short video (not embeddable, sorry) on the Higgs-Boson and string theory by Dr. Michio Kaku.  Comments?

Posted by Goodhart 6 years ago

Checking Theories

In this topic, place your theories of some chemistry experiments in the comments section, starting with this one. To start with, Fe + 2H2O --> FeO2 + 2H...Place iron fillings to fill 1/3 of a water bottle. Fill the rest with water, and place a balloon on top. Wait X days/weeks/months. The water reacts with the iron to extract the oxygen from the water, leaving only hydrogen, and rust in the products. In the reactants, the hydrogen was bonded to the oxygen.Will someone tell me if this works? The energy that bonds this is the potential energy in the water.

Posted by PKTraceur 9 years ago

Which is more likely to work and which is more based on fact, the modified alcubeirre warp theory or the hiem hyperdrive Answered

Which is more likely to work, the alcubierre drive which allows for superluminal travel using a Jupiter's mass of energy or the superconducting gravito-photon effect that powers the theoretical hiem theory hyperdrive?

Asked by amelius 7 years ago

will this theory work for an assassins creed hidden blade? Answered

i built this theory but i did not try will it work? note : the circles are springs , strong ones note : the back end's reach = the long of the blade gets out + the tall of half your arm

Asked by top.boy 6 years ago

need help with ir object detecor (reflect theory)?

Hi i'm working on a small project using iri want to make an object detector for detecting people who stand in front of a door i don't want to use laser or ir beam cut theory i want to use reflecting theory so that the sender and reciver be in the same side just as supermarkets doors i have searched for many circuits but they all use cut theory this site is my local store that have parts in my country

Asked by aessam1 7 years ago

My "theory"!!!!!!!!!!!

"The world was created in 7 days" Is one "day" for us, one day for God? 1 day for God could be 1 billion years or something.

Posted by assasin 11 years ago

if we had two moons how would that in theory effect earth? Answered

Gravitational differences, water, magnetic poles anything?

Asked by ismael01 6 years ago

Scientific Theory

I am working on a scientific theory and I need a little help. I have 2 car batteries in series to create 24v need to power an electric motor. The motor is 14.5 amps and I need a way to control the amperage from the car batteries to the motor. Any help would be greatly appreciated.

Posted by Ice Dragon 5 years ago

What is the definition of "matter" according to the string theory? Answered

Hello!  I have recently studied about the string theory. Now what I have understood about it so far is that very small particles like the one's that make up neutrons and protons are actually made up of "strings" that vibrate in 10 dimensions at particular frequencies which determine the nature of the particles that they form. I also came to know that "strings" themselves are weird distortions of space-time.   Now I don't know if all that information is correct or not. So my question is that according to it, it would mean that matter itself is a distortion of space-time, is this true?

Asked by Wisaam 5 years ago

assassins creed hidden blade theory

Can someone please send me designs for the assassins creed hidden blade i want a real design not a paper cutout or a link to a real design

Posted by mr.militarymaster 6 years ago

Question about theory.? Answered

I have a question about the one pot that you have above with the sliding paper clip showing the voltage changing from low to high. Should the voltage reading be higher to the negative side (black wire) of the pot, and lower as it is pushed to the positive side (red wire ) of the pot?

Asked by JosephW33 1 year ago

New Theory For A Pump Action Gun

The black is the gun body, the red is the ramrod, the yellow is the pump, the green are the wheels, the blue could be either string or fishing line. Theoreticly i think that this gun can hold as much power as you can pump if you use high quality fishing line and you have built a strong gun body. I think that this could be a very powerful shotgun if built right. i myself have tried to do this many times through but have never sucseded. I would like to see someone give a shot at this one. I looked around extinsivly and could find no gun like this. I give a thousand congrates to whoever sucsedes in building this. Also if someone does happen to build it I would like partial credit and instructions. I would like to thank all of you for taking you time to read this through.

Posted by TheAwesomestDude 6 years ago

Basic DC (direct current) theory and practice for newbies

Hey everyone, as you may have guessed - i'm a newbie to DC theory! Backstory: after graduating i said 'forget it' to a proper job and moved to Australia to travel. i bought a converted camper van that has an auxillary battery for (whatever), and it looks like it runs off 12 volt dc! the Question: how does DC power work, for me and all those newbies out there putting along on the other side of the planet! -cheers, adrian

Posted by adritek 10 years ago


Anyone  got any theories on how the xylobands work? Especially at the £3 a piece mark?

Posted by kelvinmead 5 years ago

"Kiteman" proves theory of Reverse Evolution!!!!!

Http://, my mistake. With the headlines, and the (initially) grainy photos, I thought this was Kiteman- Demonstrating the FACT that intelligent beings can "de-volve" into funky chickens.

Posted by skunkbait 8 years ago

Why did the duck go up? Any theories? Skip ahead to 4:57. What he refers to as string appears to be an elastic material. He pulls up and it goes up. He pulls down and it goes up. The video is supposed to be about electrostatic toys.

Asked by Vorenus 7 years ago

Taylor Couette

Does anyone know how to make the Taylor-Couette apparatus (as illustrated here) ?

Posted by piimapoika 8 years ago

Nova's Elegant Universe

Nova's Elegant Universe is a very well made scientific documentary about string theory. If any of you have been interested in The Fabric of the Cosmos by Brian Greene but don't have a chance to sit down and read something. This is for you.String theory is trying to unify our understanding of everything through one equation, if you think that is interesting then: Click here to watch the entire series // More Brian Green at TED here \\

Posted by lamedust 10 years ago

Is it possible to create a magnetic difference engine using stirling theory? Instead of hot and cold can strong and weak Answered

I just got finished building a stirling engine using plans from instructables author: thecheatscalc published dec 17 2007. The stirling engine is a heat difference engine. Is it possible to create a magnetic difference engine using stirling theory? I was thinking instead of hot and cold north and south or strong and weak..?

Asked by bazalaz 9 years ago

Can the human body be used as a battery?

My son and I are working on his science fair project which is to light a light bulb using a piece of copper pipe, a piece of galvanized pipe, and two wires with alligator clips to connect the light bulb.  The theory is that holding the two pipes in ones hands, the  body will create enough current to light the bulb.  We have not had any success yet.  Even wetting our hands had no noticeable affect.  Any ideas?  Is this a plausible theory?

Asked by speedway1839 8 years ago

Air Compressor/Vacuum Pump

I have a theory: You have your supply of compressed air. You connect that by hose to one branch of a y-connector. The other branch is connected to a hose that goes into some sort of fluid that you want to move from one vessel to another. The trunk of the y is your exhaust (in theory). So now I give, say, 15 psi out of my air supply and that shoud drag my fluid out of its vessel through the y connector to the destination of my choosing. Would that work?

Posted by flagrantfouler 9 years ago

4 Reasons why we believe in Conspiracy theories

Did NASA really land on the moon?Did the government cover-up involvement in the Sept. 11, 2001 terrorist attacks?Is Elvis still alive and kicking? What about Michael Jackson?Was John F. Kennedy assassinated at the hands of multiple shooters?Do the Freemasons control the United States?A small but fervent group of people believe there was more than included in historical record about the aforementioned events. Conspiracies, they call them. And every generation has its own.Some of them turn about to be true, after all: Pearl Harbor was a Japanese conspiracy and Nixon’s Watergate break-in was a coverup.But with so few that turn out to be true, why do people believe in conspiracies?HERE is the link to the Rest of the story.And one final note:so, NOW we know who was on the grassy knoll and shot JFK LOL It was JFK himself !!!

Posted by Goodhart 8 years ago

This is what happens when you're too lazy to buy a real webcam:

Not practical at all and in theory this was more expensive than buying a real webcam but it does work:

Posted by DJ Radio 7 years ago

possibility of Wave Change?

This theory states (my own be exact) that a certain wavelength can become an amorphous solid using a certain gas, a friend of mine agreed with me. What is your opinion on this matter?

Posted by crc09 8 years ago

Hydrogen as a fuel?

It's easy to separate hydrogen and oxygen from water. If you mix them together it doesn't become water until it is burnt. In theory you could make a water rocket from gases. But in reality...

Posted by Princess_Mellow 10 years ago

What the Hell is going on Here? Answered

I was looking at lowney's profile and this is what I found. I have no Idea how this happened but I would like to know does anyone have any theories?

Asked by Fred the Penguin 8 years ago

What do I need to know about high voltage? Answered

I'm planning on doing a little bit of high-voltage work ( see my plasma cutter question), and I know most of the theory ( except why HV AC in power lines wants to go to Earth ground--any answers to that are welcome. I have my own theories, but...), but I have really no practical experience at all with high ( 50,000 volts) voltage, i.e. what gauge of wire to use, what gloves to wear, how to ground a metal container, etc. Any advice is welcome. Thanks!

Asked by mad magoo 9 years ago

Can anyone recommend an online resource for very entry level IC and general electronic design?

I've taken classes that go into theory and the mathematics behind it, but what I'm looking for is how you go about designing for a task.

Asked by deathromp 9 years ago